Technical Field
This invention relates to a stretchable circuit board.
Related Art
There have been growing interests in biosensor and biological information monitor, in the recent market of wearable device and medical device. For example in the sport industry, trials have been made on precise quantification of physical motion, aiming at further enhancing physical abilities and skills of athletes. In some cases, wearable biosensors for sensing motion of living body have been applied. Meanwhile in the medical industry, trials have been made on sensing vital signs (biological information) including electrocardiogram, heart rate, blood pressure and body temperature, for the purpose of treatment and prevention of disease. For this purpose, the biological information monitor for detecting biological information has occasionally been applied. The biosensor and the biological information monitor are typically provided to clothes or fitting, so that sensing and monitoring are enabled when the clothes or fitting are worn.
Since, however, the clothes or fitting slightly shifts from the human body as the human body moves, so that the biosensor or the biological information monitor provided to the clothes or fitting would be misaligned from a target point of the living body, considerably lowering accuracy of sensing or monitoring.
The problems above may be suppressed by placing the biosensor or the biological information monitor directly onto the human body. In recent years, a technology called stretchable electronics, using an in-plane stretchable base and interconnects, has been investigated, and has come to propose a circuit board capable of stretching and contracting conforming to the motion of joint or the like of the human body.
Regarding this sort of stretchable circuit board, JP-A-2014-236103 describes a circuit board composed of a stretchable base, and an electro-conductive pattern containing an electro-conductive particle and an elastomer, thereby being made stretchable as a whole. Meanwhile, JP-A-2014-162124 describes a stretchable circuit board in which islands, formed by printing to give a film composed of a material having the Young's modulus larger than that of a stretchable base, are embedded in the base. Each island has a device mounted thereon, and the islands are mutually connected with stretchable interconnects. According to the description, with this configuration, the device and the interconnects which lie across boundaries between the islands and the base may be prevented from being broken, even if the stretchable base stretches or contracts.    [Patent Literature 1] JP-A-2014-236103    [Patent Literature 2] JP-A-2014-162124
In such stretchable circuit board described above, it is necessary to pay special attention to provide the interconnect part and other various constituents on the stretchable base, so as to tolerate the stretching and contraction. Since, however, in-plane rigidity or in-plane Young's modulus vary from constituent to constituent depending on their constitutive materials or thickness, so that the stretchable circuit board sometimes will not be uniform as a whole in terms of stretchability. In such case, stress during stretching and contraction may be concentrated locally, and thereby the interconnect part in such location may become more susceptible to breakage.